m68k: Fix writew(), writel(), readw(), readl() endianness for classic m68k

m68k: Fix writew(), writel(), readw(), readl() endianness for classic m68k

In Linux these are meant to read a little-endian value and swap
to the CPU endian.

In u-boot for m68k this is currently broken and prevents
virtio-mmio from functioning.

This change is only for classic m68k. Coldfire has read big-endian,
no swap for these in u-boot and Linux and existing drivers probably
depend on this.

Tested-by: Angelo Dureghello <angelo@kernel-space.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Acked-by: Angelo Dureghello <angelo@kernel-space.org>
Signed-off-by: Daniel Palmer <daniel@thingy.jp>